The laboratory has been investigating the role of endogenous cytokines as mediators of clinical conditions that are important in the management of cancer patients. Using a monoclonal antibody against the IL-I receptor, we have characterized the prophylactic and therapeutic effects of this antibody in a murine model of endotoxic shock and observed that the therapeutic effects of the IL-I receptor antibody are closely related to a decrease in systemic levels of IL-6. Furthermore, combined treatment using antibodies against TNF and IL-I is no more efficacious than either antibody alone. This observation has significant implications for the use of combined anticytokine immunotherapy in the treatment of inflammatory diseases. The laboratory has also identified differentiation factor (D-factor), also known as leukemia inhibitory factor, as an important inflammatory mediator in chronic and acute inflammatory conditions. Using RT-PCR, we have detected increased gene expression for D-factor in a variety of murine tissues after the administration of LPS or TNF. We have also observed increased gene expression in tumor bearing mice. The laboratory has developed a highly specific polyclonal rabbit anti-mouse antibody (DF Ab). Passive immunization of mice against D-factor will completely prevent LPS or TNF induced lethality. The protective effects are associated with marked decreases in circulating levels of IL-I and IL-6 after LPS indicating that the presence of D-factor activity is critical for the release of inflammatory mediators. Passive immunization against D-factor in tumor bearing mice will prevent the lethal but not therapeutic (antitumor) effects of TNF. We are currently evaluating the physiological effects of D-factor in a variety of disease states using in vitro models. Specifically we are coculturing a murine macrophage cell line with conditioned supernatant from tumors as well as with LPS or TNF with and without the D-factor antibody. We have characterized the effect of D-factor on LPL activity in murine 3T3-Ll adipocytes, on in vitro model of cachexia. In the murine adipocyte D-factor causes a profound decrease in LPL activity and works synergistically with TNF. These ongoing studies will continue to elucidate the mechanisms by which D-factor contributes to the manifestations of various disease states.